When did HP retire their two-shot molded keys?

[EdS2]

It's possible I'm mistaken about the 31E (although I think the question of the history is still interesting.)

This photo was my starting point - I don't have a 31E:


You'll notice two of the keys are worn blank, then had been relabelled by hand and that had (of course) also worn blank.

The observation that two-shot keys were sometimes overprinted to balance production is also an interesting one.